The enabling of the transfer of control of a computer system between a piece of firmware (software that is at least initially stored in nonvolatile memory within the hardware making up the computer system—sometimes referred to as embedded software) and an operating system is widely known where provision has been made for such a transfer of control within both the piece of firmware and the operating system. This is usually seen where both the computer system, including the firmware, and operating system are created by the same manufacturer.
However, a far greater number of computer systems and their firmware are created by manufacturers having no connection with the manufacturers of the operating systems that are typically executed on those computer systems, especially in the case of personal computers where end users are accustomed to having pieces of hardware and software provided by numerous unrelated manufacturers. In such cases, the operating systems are often created with the inherent assumption that once the operating system begins to be executed by the computer system, the operating system will not transfer control of the computer system to any other piece of software. Even in situations where an operating system created by a manufacturer separate from that of a computer system ostensibly makes provision for transferring control to a piece of firmware provided by the manufacturer of the computer system for a specific limited purpose, such as supporting power management, it is often the case that the manufacturer of the operating system discourages the use of such a provision, and it is frequently the case that such a provision is implemented with sufficient limitations and/or undesirable characteristics that use of such a provision is widely deemed to be undesirable.
Indeed, all known present operating systems making some provision for firmware are designed to not allow for the execution of just any form of firmware. Such provisions, where they exist, are designed to support the carrying out of only narrowly defined functions by firmware. An example of such limited provision may be found in the Advanced Configuration and Power Interface (ACPI) Specification, a specification of a standard for power management agreed to by numerous manufacturers of hardware and software commonly associated with personal computer systems. ACPI defines a provision for the use of firmware to carry out only very specific power management functions to support unique pieces of hardware.
The end result in cases where the computer system, along with its firmware, and the operating system are created by different manufacturers is that the end user of such a computer system is never provided with the option of being able to temporarily halt execution of the operating system in order to make use of a piece of firmware unrelated to the operating system without shutting down and restarting the computer system. This is the case because the opportunity to execute such firmware exists only immediately after such computer systems are powered on or restarted by the end user, and before execution of the operating system begins.